This invention relates in general to machines for working sheet metal, and more particularly to an improvement to machines of the double bar variety which form reversely bent cleat edges on sheet metal.
The duct work in most residential, commercial, and industrial buildings is formed from sheet metal with each duct usually consisting of individual duct sections coupled together at their ends. To provide a coupling, the ends of adjacent duct sections are provided with reverse flanges which are more commonly referred to as cleat edges. Drive cleats are passed over the cleat edges and interlock with them to hold the duct sections together. More specifically, the flanges or cleat edges on the duct sections are bent backwardly at 180.degree., while the drive cleat has flanges which are turned inwardly at 180.degree.. The flanges of the adjacent ducts and the flanges of the cleat interlock, thereby preventing the adjacent duct sections from pulling apart.
The cleat edges of the duct sections are normally machine formed, although they may be formed by hand operated tools. One machine for bending such cleat edges is disclosed in U.S. Pat. No. 2,973,796, issued Mar. 7, 1961.
The cleat edge forming machine of U.S. Pat. No. 2,973,796 is of the double wiper bar variety. Basically, it includes (FIGS. 1 and 2) a plate-like anvil, an upper wiper bar having its axis of rotation located directly beyond the end edge of the anvil and aligned therewith, and a lower wiper bar having its axis of rotation directly below the anvil. The duct section is placed on the anvil with the end of one of its walls projected beyond the end edge of the anvil. Then the wiper bars are revolved, and they rotate in unison, with the upper leading the lower insofar as contact with the duct wall is concerned. The timing and location of the wiper bars are such that the upper bar first strikes the outwardly projecting portion of the duct wall and turns downwardly at 90.degree.. Then the lower wiper bar strikes the downwardly turned portion and turns it another 90.degree.. Indeed, the end of the duct wall is turned a full 180.degree. so that after the lower wiper bar passes beyond the turned portion, it is located beneath the anvil.
The upper wiper bar lies directly beyond the end of the anvil and is provided with a gauging segment, which when located opposite the edge of the anvil forms a stop against which the wall of the duct section may be brought (FIG. 1). This insures that a precisely measured portion of the duct wall will project beyond the anvil so that the cleat edge which is formed on the duct wall has the correct width.
The upper wiper bar has two rest positions. In the first (FIG. 1) the gauging segment is located directly beyond the end of the anvil so that projection of the duct wall is easily gauged. In the second (FIG. 2) the gauging portion is located away from the end edge of the anvil so that a greater distance exists between that end edge and the upper wiper bar. This enables the cleat edge to be disengaged from the anvil without being obstructed by the upper wiper bar.
At the completion of a bending cycle, the upper wiper bar is in its second rest position, that is, the one in which the greatest spacing exists between the first wiper bar and the anvil (FIG. 2). This enables the duct section to be easily disengaged and removed. However, before another duct wall may be bent, the upper wiper bar must be rotated to its first rest position, which is about 45.degree. from the second, so that the gauging may be accomplished (FIG. 1). This constitutes an extra step in the operation and therefore consumes valuable time. Furthermore, it is not uncommon for an inattentive workman to forget the step altogether, in which case the projected portion of the duct wall is gauged against the wrong surface of the upper bar. Indeed, too much of the duct wall projects beyond the anvil. The excessive metal usually jams the machine and jams of this nature are often exceedingly difficult to clear. Sometimes, they necessitate partial disassembly of the machine.